The distal sesamoidean impar ligament: Comparison between its appearance on magnetic resonance imaging and histology of the axial third of the ligament

Reasons for performing study: There is limited knowledge about the interpretation of alterations in the distal sesamoidean impar ligament (DSIL) detected using magnetic resonance imaging (MRI) and their correlation with histopathology. Hypotheses: There would be: 1) a correlation between histopathology and MRI findings; and 2) a relationship between MR abnormalities at the origin and the insertion of the DSIL, between insertion and body; and origin and body. Methods: Fifty limbs from 28 horses were examined using high‐field MRI and histopathology. MR abnormalities of the DSIL, its origin on the navicular bone and its insertion on the distal phalanx were graded. Sections of the axial third of the DSIL were examined histologically and graded according to fibre orientation, integrity of fibroblasts, collagen architecture and vascularity. Associations between MRI and histology findings were tested by Spearman rank correlation and Chi‐squared tests. Results: There were significant correlations between the presence of a cystic structure in the distal third of the navicular bone, or a distal border fragment, or increased signal intensity in fat suppressed images at the insertion of the DSIL on the distal phalanx and the histological grade of the body of the DSIL. There were significant associations between a cystic structure in the distal third of the navicular bone and the presence of either a distal border fragment or entheseous new bone at the insertion of the DSIL, swelling of the DSIL and increased signal intensity in the DSIL in fat suppressed images; between distal elongation of the flexor border of the navicular bone and the presence of one or more distal border fragments and between swelling of the body of the DSIL and irregularity of its palmar border or increased signal intensity in fat suppressed images in the DSIL. Conclusions and clinical relevance: The presence of a cystic structure in the distal third of the navicular bone detected using MRI, a distal border fragment or increased signal intensity at the insertion of the DSIL are suggestive of significant alterations in the infrastructure of the DSIL.     

Microanatomic characteristics of the insertion of the distal sesamoidean impar ligament and deep digital flexor tendon on the distal phalanx in healthy feet obtained from horses

OBJECTIVE: To describe microanatomic characteristics of the insertion of the aistal sesamoidean impar ligament (DSIL) and deep digital flexor tendon (DDFT) on the distal phalanx in horses. SAMPLE POPULATION: Healthy feet obtained from 62 horses of various breeds. PROCEDURE: Feet from 23 horses were used to histologically examine the insertion of the DSIL and DDFT (n = 7), its vasculature (10), and neural elements (6). In 39 other horses, the insertion zone was examined for proteoglycan. RESULTS: The insertion of the DSIL and dorsal half of the DDFT contained bundles of collagen fibers with intervening loose connective tissue septa with arteriovenous complexes (AVC) and nerve fibers. Microscopic examination revealed adaptive changes in the insertion with regard to proteoglycan content. In young adult horses, little or no staining for proteoglycans was evident, whereas in middle-aged horses, moderate proteoglycan staining was seen. Six older horses had slight proteoglycan staining at the insertion. CONCLUSIONS AND CLINICAL RELEVANCE: The study revealed that this region contained a rich neurovascular complex between the collagen bundles. A gradual increase in production of proteoglycan, evident at the insertion of the DSIL and DDFT on the distal phalanx, indicates that adaptive responses to stress rather than age alone may be the primary determining factor. These observations indicate that this insertion site may be susceptible to stress during stance and impact loading, because this region appears to be strategically situated to regulate important neurovascular functions of the foot.     

Outcome after lacerations of the superficial and deep digital flexor tendons, suspensory ligament and/or distal sesamoidean ligaments in 106 horses

Objective: To report outcome after the surgical treatment of lacerations of the superficial digital flexor tendon (SDFT), deep digital flexor tendon (DDFT), suspensory ligament (SL), and/or distal sesamoidean ligaments (DSL) in horses. Study Design: Case series. Animals: Horses (n=106) with lacerations of the SDFT, DDFT, SL, and/or DSL. Methods: Medical records (1988–2002) were reviewed for signalment, limb and tendon/ligament involvement (location and extent of injury, tendon sheath involvement), method of repair, and outcome. Results: The median age of horses was 7 years and the follow‐up time ranged from 1 to 10 years. Fifty‐five percent of horses returned to their previous level of performance, 27% to a lower level, and 18% were euthanatized. Multivariate statistical analysis demonstrated that the number of structures transected had the most significant influence on outcome. No significant association was detected between outcome and tendon sheath involvement, tendon suturing, casting, or limb affected. Fetlock hyperextension was the most significant complication. Conclusions: A high survival rate can be expected after SDFT, DDFT, SL, and/or DSL lacerations in horses, but only 55% of affected horses returned to their previous activity level. The number of structures affected was the major factor determining whether horses returned to an equal level of performance.     

Increased severity of calf pneumonia associated with the appearance of Mycoplasma bovis in a rearing herd

An increase in deaths in calves from respiratory disease from an average of 9.7 per year to 36.5 per year corresponded with the isolation of Mycoplasma bovis from the lungs. It is suggested that this mycoplasma enhanced the severity of the disease which was normally present on the farm. The characteristic microscopic lesion and demonstration of M bovis by immunoperoxidase labelling could be useful aids to diagnosis.     

Evaluation of tachykinins and their receptors to determine sensory innervation in the dorsal hoof wall and insertion of the distal sesamoidean impar ligament and deep digital flexor tendon on the distal phalanx in healthy feet of horses

OBJECTIVE: To localize substance P (SP) and neurokinin A (NKA) and their receptors in the insertion of the distal sesamoidean impar ligament (DSIL), deep digital flexor tendon (DDFT), and dorsal hoof wall of healthy feet of horses. SAMPLE POPULATION: 18 healthy feet from horses. PROCEDURE: Samples from the dorsal hoof wall and insertion of the DSIL and DDFT of 10 feet were processed for immunocytochemical analysis, using rabbit polyclonal antisera raised against SP and NKA. Tissue sections from 8 feet were incubated with 125-labeled SP to localize tachykinin receptors and their specificity and with control solutions of radioactive SP and excess nonradioactive SP to identify areas of nonspecific binding. RESULTS: Many nerves immunoreactive for SP and NKA were localized to the region of the insertion of the DSIL and DDFT and the accompanying microvasculature and arteriovenous complexes (AVC) as well as to the microvasculature of the dorsal hoof wall. Specific neurokinin 1 receptors were localized over the microvessels and AVC of the insertion zone and small microvessels of the hoof wall. CONCLUSIONS AND CLINICAL RELEVANCE: These results document that the microvasculature of the equine foot is richly innervated and has specific receptors for tachykinins. Distributions of these tachykinin receptors on the microvasculature suggest that they form an important vasodilatory mechanism for controlling blood flow through the DSILDDFT insertion and dorsal hoof wall.     

Genetic analyses of the radiographic appearance of the distal sesamoid bones in Hanoverian Warmblood horses

OBJECTIVE: To evaluate whether additive genetic correlations existed between certain aspects of the radiographic appearance of the distal sesamoid (navicular) bones (RNB) or between RNB and other types of radiographic changes in the limbs of Hanoverian Warmblood horses. ANIMALS: 5,157 horses. PROCEDURES: Quasi-linear and binary traits were defined by the appearance of canales sesamoidales (CSs) and the structure and contour of the forelimb navicular bones (NBs). Prevalences of osseous fragments in the metacarphophalangeal and metatarsophalangeal (fetlock) and tarsocrural joints and deforming arthropathy in tarsal joints were analyzed as binary traits. Genetic parameters were estimated by use of multivariate linear models. RESULTS: Heritability estimates for the RNB traits ranged from 0.10 to 0.34. Additive genetic correlations among those traits were usually close to unity. Extensive radiographic changes in the NBs, including changes in CSs and alterations in structure and contour, had correlations with less distinct radiographic changes. Negative additive genetic correlations were observed between small numbers of short and conical CSs in the central portion of the distal border of the NB and osseous fragments and arthropathy, and between most types of radiographic findings in the NBs and osseous fragments in tarsal joints. CONCLUSIONS AND CLINICAL RELEVANCE: The genetic bases for different types of RNB were not identical. The detection of correlations between normal RNB and findings of short and conical CSs versus deformed CSs and structural and contour changes warrants further study. Genetically justified distinction between physiologic and pathologic NB changes will increase the efficiency of selecting against NBs with radiographically apparent alterations.     

Ultrasonographic appearance and correlative anatomy of the soft tissues of the distal extremities in the horse

The diagnostician should be familiar with the normal ultrasound appearance (size, shape, position, and textural quality) of each structure examined. With these factors as reference points, one can describe lesions in the structure involved, the precise location and extent of the lesions, and the degree of structural compromise that is manifested. Documentation of lesions of tendons and ligaments enables one to make an accurate diagnosis and a more precise prognosis. Serial examination during the healing phases allows for a more accurate prediction as to when the structure in question can withstand athletic challenge.     

Evaluation of an arthroscopic approach for transection of the equine collateral sesamoidean ligament

Objective: To evaluate: (1) an arthroscopic technique for transection of the collateral sesamoidean ligament (CSL); and (2) the healing response using magnetic resonance (MR) and microscopic examination. Study Design: Experimental study. Animals: Adult horses (n=6). Methods: Six sound horses with normal front foot radiographic and MR examinations were used. Lameness examination was performed before surgery and monthly for 12 months. Front foot radiography was performed at 180 and 360 days after surgery. Front foot MR was performed before, and at 7, 90, 180, and 360 days after surgery. Arthroscopic CSL desmotomy was performed on 1 forelimb. Gross and microscopic examination was performed on the CSL from both forelimbs at 360 days after surgery. Lameness scores were compared over time using the nonparametric Friedman's test for paired groups. CSL measurements were compared using paired t‐tests with a 2‐tailed significance level of P<.05. Results: Radiographs remained normal throughout study period. Surgery resulted in lameness on the operated limb for up to 2 months, after which all horses returned to soundness. CSL transection was confirmed during arthroscopy and with MR examination 7 days after surgery. Gross and microscopic evaluation confirmed ligament healing. Conclusions: CSL desmotomy resulted in short‐term lameness after surgery followed by healing of the CSL confirmed by gross and microscopic analysis.     

Time of appearance of esterase-positive alveolar macrophages in bovine fetal lung

Bovine fetal lung tissue was examined histochemically, using alpha-naphthyl butyrate (nonspecific method), to detect the presence of esterase-positive pulmonary alveolar macrophages (PAM). Positively stained PAM were first seen in the alveolar septa and lumina of the lungs of 4 of 8 fetuses 240 days old. Macrophages (n = 100) in 240-day-old fetuses were 6.74 +/- 0.07 microm, and in most cells, esterase-positive granules were sparsely distributed in the cytoplasm. In 10 fetuses 250 days old, the alveolar septa and lumina of lungs contained positively stained macrophages, as did those of all older fetal lungs examined. Compared with macrophages of the 240-day-old fetuses, those (n = 50) of 250-day-old fetuses were significantly larger, 7.32 +/- 0.10 micron (P less than 0.0001), and esterase-positive granules were heavily distributed throughout the cytoplasm. In all fetal lungs, T lymphocytes contained a single, small, esterase-positive granule, compared with the numerous diffuse esterase-positive granules in PAM. Type-II pneumonocytes with well-developed lamellar bodies had no evidence of positive nonspecific esterase reaction in lungs.     

Collateral desmitis of the distal interphalangeal joint in conjunction with concurrent ossification of the cartilages of the foot in nine horses

The purpose of this study was to describe the frequency of occurrence of severe ossification of the collateral cartilages (sidebone) coexistent with collateral desmitis of the distal interphalangeal joint (DIPJ) in lame horses. Sidebone was diagnosed and graded on standard radiographs and soft tissue injuries of the foot were diagnosed using standing low‐field magnetic resonance imaging (MRI). Of 15 horses with forelimb lameness and severe sidebone, 9 had evidence of concurrent collateral desmitis of the DIPJ. All 15 horses had damage to other structures (including the deep digital flexor tendon, distal sesamoidean impar ligament, collateral sesamoidean ligament, navicular bone and distal phalanx) within the affected feet as identified on MRI. The clinical and pathophysiological significance of concurrent collateral desmitis of the DIPJ and sidebone is currently uncertain. However, this study shows that injuries to multiple structures within the foot are common and that collateral desmitis of the distal interphalangeal joint is frequently seen in lame horses in conjunction with severe ossification of the collateral cartilages.